The majority of hemodialyzed patients suffer from sleep disturbances. In the present study the prevalence of sleep apnea syndrome in hemodialyzed patients with end-stage renal disease (ESRD-patients) was investigated by the survey, Epworth Sleepiness Scale (ESS), and polysomnography (PSG). Sixty-one patients: 24 women and 37 men were involved in the study. All subjects participated in the first part of the study consisting of the survey and ESS. The second and third parts consisted of nighttime PSG, performed the night after hemodialysis (17 patients) and between hemodialyses (11 patients). Eleven out of the 61 patients had the symptoms of sleep apnea and heavy daily sleepiness. Eleven subjects were involved in the double PSG study: after and between hemodialyses. Obstructive sleep apnea was found in 7 of those patients during both nights analyzed. Our results confirm the occurrence of sleep disorders in ESRD-patients. Hemodialysis does not change the prevalence of obstructive sleep apnea in chronic renal disease.